car issues

I wanted to add a car to my game. The way I did this initially is to take the default car "buggy" and change the dts it loaded to my own in the source code. However, when I do this the engine fails to register that the car even exists.

I understand that fully rigging a car may be much more complicated than this. Can anyone help me with the issues involved with creating a car extended from "wheeled vehicle" or the "default car"?

Thanks